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What is LED

LED stands for Light Emitting Diode
An LED is a special type of semiconductor diode. Like a normal diode, it consists of a chip of semi conducting material impregnated, or doped, with impurities to create a structure called a p-n junction. As in other diodes, current flows easily from the p-side or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers-electrons and electron holes flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon as it does so. LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever shorter wavelengths, producing light in a variety of colors.

LEDs are usually built on a n-type substrate, with electrode attached to the p-type layer deposited on its surface. P-type substrate. Substrates that are transparent to the emitted wavelength, and backed by a reflective layer, increase the LED efficiency. The refractive index of the package material should match the index of the semiconductor, otherwise the produced light gets partially reflected back into the semiconductor, where it gets absorbed and turns into additional heat.

Conventional LEDs are made from a variety of inorganic semiconductor materials, producing the following colors:

Aluminium gallium arsenide (AlGaAs) -- red and infrared

Aluminium gallium phosphide (AlGaP) – green

Aluminium gallium indium phosphide (AlGaInP) – high-brightness orange-red, orange, yellow, and green

Gallium arsenide phosphide (GaAsP) – Red, orange-red, orange, and yellow

Gallium phosphide (GaP) – red, yellow and green

Gallium nitride (GaN) – green, pure green (or emerald green), and blue

Indium gallium nitride (InGaN) – near ultraviolet, bluish-green and blue

Silicon carbide (SiC) as substrate-blue

Silicon (Si) as substrate-blue (under development)

Sapphire (AI2O3) as substrate-blue

Zinc selenide (ZnSe)-blue

Diamond (C) – ultraviolet

Aluminium nitride (AIN), aluminium gallium nitride (AlGaN)-near to far ultraviolet

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